Bone is a supporting material for the body's framework and serves to conserve the necessary bone mass and structure. Bone also functions as a reservoir of calcium (Ca2+) or the like, and plays an important role in maintaining the calcium level in the blood. To this end, bone undergoes continuous degradation and remodeling. Thus, bone is in a dynamic steady state, which maintains a delicate balance by continuously performing both bone resorption and bone formation. When the balance between bone resorption and bone formation is disrupted, the degree of bone resorption is relatively higher than that of bone formation, which may lead to osteoporosis, a condition which causes reduction in bone density or bone mass, resulting in decrease in bone strength. This is a disease which frequently occurs in middle-aged or elderly women.
Osteoporosis is a disease, which results from a disturbance in the balance between bone resorption and bone formation, and is caused by having a higher degree of bone resorption relative to that of bone formation. Osteoporosis reduces calcification of bone tissues, and decreases the level of the compact substances in the bone, which broadens the marrow cavity. As osteoporosis progresses, bone becomes brittle, and bone fracture may easily occur even with a small impact. Bone is a steady state structure, in which the bone formation by osteoblast and the bone resorption by osteoclast occur continuously.
Previous studies on osteoporosis have focused mainly on the metabolism of bone minerals, such as calcium and phosphorus. However, such studies did not provide sufficient findings on the mechanisms of osteoporosis.
Bone fracture is associated with an increased mortality rate of patients with osteoporosis, and also causes serious problems such as negative impact on patient's quality of life. Thus, various strategies have been established to produce drugs capable of preventing loss of bone density and bone fracture.
To date, bisphosphonate (alendronate, etidronate), hormones (raloxifen), vitamin D, calcitonin, calcium agents, or the like have been used as an anti-osteoporotic agent, and Forteo™, a form of parathyroid hormone responsible for bone formation, is currently used to treat advanced osteoporosis. However, they are known to have adverse effects. Specifically, hormone agents must be administered throughout patient's life and in the case of long-term administration, side effects such as breast cancer, uterus cancer, gallstones and thrombosis may be induced. Vitamin D agents are expensive and show little efficacy, and calcitonin agents are also very expensive and difficult to administer. Calcium agents have few side effects, but their effects are restricted to the prevention of osteoporosis, not the treatment itself. Forteo™, a commercially available parathyroid hormone, has an advantage in that it stimulates bone formation, whereas the known drugs are restricted to the prevention of bone resorption. However, Forteo™ should be given as a daily injection for a long period of time and may increase the risk of osteosarcoma. Its application is also restricted due to the high price.
A bisphosphonate drug, alendronate or risedronate, represented by the following Formula, has been widely used for the treatment of osteoporosis and shown to increase bone density and prevent fractures as an inhibitor of bone resorption. Owing to advantages of oral administration and lower cost, it has been widely used in clinical fields for the treatment of calcium metabolic disorders including osteoporosis.
However, bisphosphonate agents show low absorptivity and may induce esophagitis, and thus should be taken with a sufficient amount of water before meals. In addition, patients should wait at least 30 minutes before ingesting other beverage or food and avoid lying down for a predetermined time following administration. They are also reported to increase the risk of hypocalcemia. Recent studies have suggested problems such as reduction in bone turnover rate due to excessive inhibition of bone resorption, inhibition of bone formation, gastrointestinal disorders and osteonecrosis of the jaw. Furthermore, it is recently reported that its long term administration increases the risk of bone fractures (Andrew S Neviaser et al, Journal of Othopaedic Trauma, 2008, 22(5), 346˜350).
As described above, the current therapeutic agents for osteoporosis are not those which act on both bone resorption and formation. Accordingly, in order to treat osteoporosis, there is a need for the development of drugs and therapies which lead to balanced increase in the bone mass and improvement of bone quality and thus reduce the risk of bone fractures.
To overcome the above drawbacks and improve the clinical efficacy, many studies have been made, and recent studies suggested combination therapy of a bone resorption inhibitor and a commercially available parathyroid hormone that stimulates bone formation. The detailed description thereof is as follows.
The combination therapy of alendronate and other bone resorption inhibitor are exemplified by alendronate and estrogen (literature—Lindsay et al, J. Clin. Endocrinol. Metab. 84, 3073-3081 (1999)), alendronate and raloxifene (literature—Johnell et al, J. Clin. Endocrinol. Metab. 87, 985-992 (2002)), alendronate and HRT (hormone replacement therapy) (literature—Greenspan et al, JAMA, 289, 2525-2533 (2003)), and alendronate and calcitriol (WO 01/28564). These studies demonstrated that the combination therapy showed an increase in bone density, compared to their individual administration, but no reduction in the risk of bone fracture. Moreover, problems including reduction in bone turnover rate due to inhibitory effect on bone resorption and inhibition of bone formation still remain, even though there are differences between their mechanisms. Thus, there are needs for considerations and further studies regarding the therapies.
In this regard, there was a trial of combination therapy with a bone formation stimulator, which was intended to reduce inhibitory effect on bone formation and adverse effects of alendronate. Combination therapy of alendronate with a parathyroid hormone is exemplified by two literatures: The effects of parathyroid hormone and alendronate in combination in postmenopausal osteoporosis (literature—Black et al, N. Eng. J. Med. 349, 1207-1215, (2003)) and in elderly men with osteoporosis (literature—Finkelstein et al, N. Eng. J. Med. 349, 1216-1226, (2003)). However, the literatures did not demonstrate the increase in bone density, compared to their individual administration. In this regard, some researchers suggested the possibility that a strong bone resorption inhibitor, alendronate counteracts the stimulating effect of parathyroid hormone. Subsequently, a sequential administration of two drugs has been tried, but further studies are still needed for a meaningful clinical outcome.
The inventors have already disclosed the therapeuric use of the benzamidine derivatives in osteoporosis in Korea Patent No. 705875, Korea Patent No. 875596, and Korea Patent Application No. 2008-0073710.
The present inventors have also studied the method to increase the prophylactic or therapeutic effect of the benzamidine compounds of Formula I or salt thereof, by the combined administration with other compounds, and developed the present compositions with an improved effect over the the individual administration that can be used in the prevention and treatment of osteopossis.